The story of the Fortress of Carmignano kept the pace with the town's one. In effect, its origins date to 998, the year when the then "curtis" of Carmignano and the territories annexed to the Bishopric of Bologna were donated. According to historians, the original nucleus of the fortification developed at that time.

In any case, the year the stronghold was born has been conventionally established to 1125, when Pistoia conquered the village again after the Florentines' irruption ousted the bishop Ildebrando's seigniory. Between 1125 and 1138, the most meaningful reinforcement works took place. In the middle of the works, the inhabitants of Pistoia also had to face the Fabbroni, the rulers of Signa who also succeeded into getting possession of the Stronghold for a short time and abandoned it hastily after some months.
Between the XII and the XIII centuries, numerous battles were fought in front of the fortress's walls. The inhabitants of Pistoia, on one side, supported by the imperial monarchy that had often reiterated their bishop's potestà on the fortress, and the inhabitants of Prato and the Florentines, on the other, confronted each other here.
The year 1228 ideally closed this epoch of clashes with the Florentines entering the town. Nevertheless, in 1301 already, after the coup by the "black" Guelphs machinated by Boniface VIII and by the king of France, the fights for the possession of the castle started to take place again.
In 1325, the inhabitants of Carmignano, oppressed by Filippo Tedici's tyranny, called Florence back to help them, but Castruccio Castracani, a Ghibelline lord among the most powerful in Northern Tuscany, interfered between the city and the definitive dominion on the stronghold. He conquered the town but, fortunately, for the inhabitants of Carmignano, he did not order the dismantling of the fortress, as he used to do after winning in the other battles of his life.
Therefore, when Florence seized it in 1343, the stronghold was in excellent conditions since Castracani had further reinforced it. With the re-establishment of peace in the area under the aegis of the Republic, the Fortress of Carmignano became the seat of a town-hall and housed the Palazzo Pretorio that was first restored in 1621.
In 1820, a new fight for the possession of the castle between the free town and the Cremoncini, who got it for thirty years, started. In the XX century, the Petroni bought the fortress and they ceded it to the commander Umberto Bigagli. Finally, only in 1990, the town got possession of the Fortress of Carmignano again.